A piezoelectric motor uses a piezoelectric vibrator to transduce electrical energy into kinetic energy that the motor transmits to a moveable body to which the motor is coupled. The motor is generally coupled to a body that it moves by resiliently pressing the motor to the body so that a surface region, hereinafter referred to as a “coupling surface”, of the piezoelectric vibrator contacts a surface region of the body. Electrodes in the motor are electrified to excite vibrations in the vibrator that cause the coupling surface to vibrate. Motion is transmitted from the vibrating coupling surface to move the body by frictional forces between the coupling surface and the surface region of the body to which the coupling surface is pressed.
The frictional forces coupling a piezoelectric motor to a body it moves might abrade the motor's coupling surface and in time might damage the coupling surface to the extent that the motor is no longer serviceable. Traveling wave piezoelectric motors that use vibrators formed from relatively soft piezoelectric material are worn out relatively quickly by abrasion. Typically, a traveling wave piezoelectric motor wears out after transmitting kinetic energy to a body that it moves that is equivalent to moving the body a cumulative “travel distance” on the order of hundreds of kilometers.
A piezoelectric standing wave motor of a type described in U.S. Pat. No. 5,453,653, to Zumeris et al, the disclosure of which is incorporated herein by reference, comprises a vibrator formed from a ceramic piezoelectric crystal. A hard wear resistant nub, hereinafter referred to as a “friction nub”, preferably formed from a hard tough ceramic material is bonded to a surface region of vibrator. To transmit motion from the vibrator to a moveable body, the friction nub, rather than a surface region of the piezoelectric crystal, is pressed to the body. The friction nub is substantially more resistant to abrasion than the piezoelectric ceramic. As a result, the operational lifetime of the motor is considerably increased over that of piezoelectric motors without such nubs. The motor is capable of being used to transmit kinetic energy to the body equivalent to travel distances well in excess of 10,000 kilometers before the friction nub wears and motor performance degrades.
Even though a friction nub extends the operational lifetime of a piezoelectric motor substantially, it is desirable to have piezoelectric motors characterized by operational lifetimes greater than operational lifetimes of piezoelectric motors that transmit motion to a body via a friction nub.